It is known that bicycles having pedal crankshaft operated brakes are subject to a lock-up condition in which the forward pedalling required to release the rear brake of the machine is impossible because the rear brake prevents rotation of the rear wheel. A solution to this problem was disclosed as long ago as 1949 in Italian Pat. No. 447,991 (Lombardi et al) which shows a bicycle with lost motion between its pedal crankshaft and its chain wheel, spring bias being provided to make the lost motion available when forward pedalling follows braking. A similar arrangement is disclosed in U.S. Pat. No. 3,888,334, issued June 10, 1975 to Mack, whilst an improved arrangement is disclosed in my own copending U.S. patent application Ser. No. 302,537 now U.S. Pat. No. 4,462,488 issued date July 31, 1984 filed Sept. 16, 1981.
This last arrangement provides effective prevention of lockup combined with smooth operation through provision of a highly progressive spring bias on the lost motion means.
All of the above arrangements utilize a chain wheel which is supported for rotation on the crankshaft either directly or through a sleeve, with some provision for restraining axial displacement of the chain wheel. A potential problem with such arrangements is that as wear occurs, the chain wheel will become a progressively looser fit on the crankshaft or sleeve, and will tend to wobble, thus both impairing operation of the bicycle and aggravating the wear problem. It is most important for commercial acceptability of a pedal crankshaft operated brake system that the necessary anti-locking device does not impair operation of the bicycle or decrease its reliability.